docs: def assert_raises_errno(exception, errno, msg_fmt="{msg}"):
      """Fail unless an exception with a specific errno is raised with the
       context.
  
      >>> with assert_raises_errno(OSError, 42):
      ...     raise OSError(42, "OS Error")
      ...
      >>> with assert_raises_errno(OSError, 44):
      ...     raise OSError(17, "OS Error")
      ...
      Traceback (most recent call last):
          ...
      AssertionError: wrong errno: 44 != 17
  
      The following msg_fmt arguments are supported:
      * msg - the default error message
      * exc_type - exception type that is expected
      * exc_name - expected exception type name
      * expected_errno -
      * actual_errno - raised errno or None if no matching exception was raised
      """
  
      def check_errno(exc):
          if errno != exc.errno:
              msg = "wrong errno: {!r} != {!r}".format(errno, exc.errno)
              fail(
                  msg_fmt.format(
                      msg=msg,
                      exc_type=exception,
                      exc_name=exception.__name__,
                      expected_errno=errno,
                      actual_errno=exc.errno,
                  )
              )
  
      context = AssertRaisesErrnoContext(exception, errno, msg_fmt)
      context.add_test(check_errno)
      return context